1. Field of the Invention
This invention relates to a touch sensor, and more particularly to a touch sensor adapted to detect a reference position for working, or a measure initiating and/or terminating position in various machine tools or a three-dimensional measuring device.
2. Description of the Prior Art
For example, when the working is to be carried out by means of a machine tool, it is highly essential to precisely determine a reference position for measuring the working position.
The setting of such a reference position has been conventionally carried out by means of a touch sensor, for example, in such a manner as shown in FIG. 1, wherein a touch sensor 2 is mounted on a working shaft 1 of a machine tool instead of a tool. The operation of a handlewheel 5 allows an object to be measured fixedly carried on a movable table 4 to abut at the end face thereof against a measuring element of the touch sensor 2, and the abutment therebetween is electrically detected and read out by a scale 6 mounted on the table 4.
Also in a measuring system, the detection of measure initiating and/or terminating positions is likewise carried out. More particularly, a touch sensor is mounted on a measuring head to electrically detect the contact between various measuring positions and the touch sensor so that the position may be read out.
There have been used many touch sensors of various constructions in such a measuring system. FIG. 2 shows a basic structure of a conventional touch sensor typically used in a measuring system for the reason that a measuring element returns to a reference position with a good repeatability.
The conventional touch sensor shown in FIG. 2 is constructed in such a manner that a measuring element 8 having a contact 8a formed at one end thereof which is adapted to abut against an object to be measured and a flange 8b formed at the other end thereof has three pin members 9 radially horizontally projected from the flange 8b, and the pin members 9 are respectively supported in three V-shaped supporting means 10 embedded in a housing. The flange 8b is constantly forced against the supporting means 10 by a spring 12 interposed between a spring bearing 11 of a pivotal mechanism and the flange 8b so that the measuring element 8 is mechanically located at a stable position of one point. In this instance, the supporting means 10 and pin 9 of each set can be deemed to form a contact mechanism together because the three supporting means 10 are deemed to be short-circuited together by the pins 9. Thus, the supporting means are connected with each other by means of wirings 13.
In the prior art touch sensor constructed as described above, when the contact 8a is abutted against an object to be measured, any one of the pins 9 is caused to separate from the corresponding supporting means 10 to open its electric circuit so that the contact between the contact 8a and an object to be measured may be detected.
However, the application of such a mechanism for supporting a measuring element as shown in FIG. 2 to a touch sensor used to set a reference position of a machine tool or the like causes the following problem.
The working operation of a machine tool is carried out after a touch sensor is mounted on a working shaft of the machine tool instead of a tool to carry out the setting of a reference position and then the touch sensor is removed from the shaft to attach the tool to the shaft.
Thus, it is essential to precisely align the center of the working shaft with that of the contact formed at the distal end of a measuring element or carry out the centering of the measuring element.
However, although the mechanism shown in FIG. 2 allows the measuring element to return to a reference position with a good repeatability, it does not include any means for aligning the center of the working shaft with that of the measuring element. Thus, it is highly difficult to carry out the centering.